We have migrated a SSRS 2008 report tot 2012. This report contains a data driven subscription and sends about 2.500 individual mails containing a PDF version of the report.In SSRS 2008 this report was running OK, but in 2012 not all mails are sentm but SSRS says no error occurred. The recipients that don't receive their mails occur randomly. When we put the PDF's on a FileShare instead of mailing directly the number of PDF's is correct.

Just some additional info.No mails are missing when using CSV as Render method. The message size is about 1 MB per mail when using PDF and seems to be a problem? However we checked our SMTP server and there are no restrictions on sizes applied. Also the log file does not contain any errors.

In SSRS 2008 everything seems to work OK. It seems to be an SSRS 2012 bug.

I know this is an old topic, but I have the proposed solution. I have contacted Microsoft about this issue and we figured out the solution for this problem.Install the following update on the SQL2012 SP1 installation.http://support.microsoft.com/kb/2894115

When using Windows SMTP server. Get rid of the SMTP limits "Limit Session Size KB" and "Limit number of messages by connection to"(my SMTP server was running on Windows 2008-R2. )